Manufacture of fibers of cellulose esters



solvent.

Patented Mar. 26, 1935;

PATENT OFFICE 1,995,804 MANUFACTURE OF rnnms or CELLULOSE ESTERS Robert Haller, Riehen, near Basel,

and Andreas Ruperti, Basel, Switzerland, assignors to the firm Society of Chemical Industry in Basic,

Basel, Switzerland No Drawing. Application May 27, 1931, Serial 6 Claims.

Fibers of organic cellulose ester can be made, as is well known, according to two fundamentally different processes. One process consists in spinning a solution of a celluloseester in a suitable The other process consists in treating with an whether natural fibers or fibers of so-called regenerated cellulose. Such esterifying agents are the anhydrides or halides of the most various organic acids, such as inter alia acetic, butyric, propionic, valeric, palmitic, benzoic, phthalic acids or the substitution products thereof. The second process. permits the production of organic esters of completely undegraded cellulose which are distinguished from the esters used in the first process by their insolubility in organic sol- .vents.

Such esters of completely undegraded cellulose, which contain more than one acyl group for each CsHmOs unit, and which are insoluble in organic solvents, may for example be produced by esterify g artificial fibers of regenerated cellulose in the presence of potassium salts of weak acids and under such conditions that the fibrous structure is retained.

It is known that fibers made by the first process may be stretched in presence of agents having a swelling action on the cellulose ester whereby, depending on the conditions, degree of stretching or the like, various properties may be imparted to the fibers, such as increased tensile strength or resistance towards treatment with hot aqueous liquids.

This invention is based on the observation that in spite of their insolubility, artificial fibers obtainable by the second process by acylating the fibers of regenerated cellulose in such a manner that more than one acyl-group for each C6H10O5- unit enter the cellulose molecule can be brought by means of suitable swelling agents into such a condition of plasticity that they can be subjected to a stretching process, whereby their titre may be reduced, and their other properties, such as feel, strength etc., can be considerably improved.

This stretching operation may follow directly after, the esterification, or may be applied to the finished goods.

Among the swelling agents which are most suitable for the purpose of the invention there maybe named:organic acids. such as dilute acetic acid or dilute formic acid, bases, such as pyridine, salt solutions, such as an aqueous ammonium thiocyanate solution etc. The following examples illustrate the invention;

esterifying agent fibers of cellulose,

In Switzerland June 2, 1930 Example 1 material which has not been stretched, has a considerably lower titre, a very much softer feel and an increased strength both in the dry and in the wet condition. The material which had been stretched until its length was 1%.; times its original length was found to have increased in strength in the wet condition by about 50 per cent.

Example 2 Cellulose artificial silk (viscose silk, Chardonnet silk or cuprammonium silk) is impregnated with a solution of potassium acetate of 55 per cent. strength, dried and heated for 1 hour on the water bath with 10 to 12 times its weight of acetic anhydride. The liquid is then run ofi whilst still hot, and the artificial silk material is extracted by means of cold glacial acetic acid, washed with water and dried. There is obtained an acetylated artificial silk whose titre exceeds that of the parent material by about 40 to 45 per cent.

The acetylated artificial silk so obtained is introduced into acetic acid of per cent. strength, and stretched until its length has increased by about 50 per cent., the titre which the material had before acetylation is thereby restored. The stretched artificial silk acquires a softer feel and improved mechanical properties, the strength increases in the wet state having increased by about 60 per cent., and the strength in the dry state by about 30 per cent. in comparison with the material before stretching. Instead of applying the stretching in aqueous acetic acid to the finished acetylated artificial silk, the stretching operation may follow directly after the acetylation and extraction with glacial acetic acid. For this purpose the glacial acetic acid remaining in the fiber after removal of the acetic anhydrideand potassium acetate may either be displaced by aqueous acetic acid, or may be diluted by addition of water to a concentration suitable for the stretching operation. In this case the material is washed out with water and dried only after the stretching operation.

Example 3 Viscose artificial silk is acetylated in the manner described in Example 2, washed out and dried. The esterified artificial silk thus obtained is introduced into an aqueous pyridinesolution of 40 per cent. strength and stretched until its length has increased by about 20 tov 50 per cent. The product resembles in its properties that obtained as described in Example 2. Instead of pyridine solution there may also be used for instance an aqueous solution of ammonium thiocyanate of 20 per cent. strength.

What we claim is:-

1. A process for improving fibers of organic esters of undegraded cellulose insoluble in organic solvents, as are obtained by esterifying artificial fibers of regenerated cellulose to such an extent that at least'the monoacidyl stage is surpassed, and in the absence of substances having a degrading action on cellulose, and under such conditions that the external form of the fiber is retained, which consists in subjecting the fibers to a stretching operation in presence of a swelling agent.

2. A process for improving fibers of organic esters of undegraded cellulose insoluble in organic solvents, as are obtained by esterifying artificial fibers of regenerated cellulose with acid anhydrides derived from such fatty acids which contain not less than two and not more than four carbon atoms to such an extent that at least the monoacidyl stage is surpassed, and in the absence of substances having a degrading action on cellulose, and under such conditions that the external form of the fiber is retained, which consists in subjecting the fibers to a stretching operation in presence of a swelling agent.

3. A process for improving fibers of organic esters of undegraded cellulose insoluble in organic solvents, as are obtained by esterifying artificial fibers of regenerated cellulose with acid anhydrides derived from such fatty acids which contain not less than twoand not more than four carbon atoms to such an extent that at least the monoacidyl stage is surpassed, and in the absence of substances having a degrading action on cellulose, and under such conditions that the external form of the fiber is retained,

which consists in subjecting the fibers to a stretching operation in presence of an aqueous solution of a fatty acid as a swelling agent.

4. A process for improving fibers of organic esters of undegraded cellulose insoluble in organic solvents, as are obtained by esterifying artificial fibers of regenerated cellulose with acid anhydrides derived from such fatty acids which contain not less than two and not more than four carbon atoms to such an extent that at least the monoacidyl stage is surpassed, and in the absence of substances having a degrading action on cellulose, and under such conditions that the external form of the fiber is retained, which consists in subjecting the fibers to a stretching operation in presence ofan aqueous solution of a fatty acid containing not more than two carbon atoms as a swelling agent.

5. A process for improving fibers of organic esters of undegraded cellulose insoluble in organic solvents, as are obtained by esterifying artificial fibers of regenerated cellulose with acetic acid anhydride to such an extent that at least the monoacidyl stage is surpassed, and in the absence of substances having a degrading action on cellulose, and under such conditions that the external form of the fiber is retained which consists in subjecting the fibers to a stretching operation in presence of an aqueous solution of a fatty acid containing not more than two carbon atoms as a swelling agent.

6. A process for improving fibers of organic esters of undegraded cellulose insoluble in organic solvents, as are obtained by esterifying artificial fibers of regenerated cellulose with butyric acid anhydride to such an extent that at least the monoacidyl stage is surpassed, and in the absence of substances having a degrading action on cellulose, and under such conditions that the external form of the fibers is retained, which consists in subjecting the fibers to a stretching operation in presence of an aqueous solution of a fatty acid containing not more than two carbon atoms as a swelling agent.

ROBERT HALLER. ANDREAS RUPERTI. 

